Such a steering unit is known, for example, from U.S. Pat. No. 4,676,334. In such a kind of hydraulic steering unit the variable orifices are arranged in a kind of Wheatstone bridge. One diagonal of the bridge is arranged between the pressure port and the tank port and the other diagonal is arranged between the two working ports.
When, for example, it is intended to steer a vehicle equipped with such a steering unit to the left, the first left orifice and the second right orifice are opened, wherein the second left orifice and the first right orifice are closed. Hydraulic fluid from the pressure port then flows through the first left orifice to the left working port and from there to a steering motor connected to the working port arrangement. Hydraulic fluid displaced from the steering motor flows back through the right working port and the right working flow path to the second right orifice. When passing the second right orifice the fluid is returned to the tank flow path and from there to the tank port.